JP2010162728A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve such a problem that it is impossible to sufficiently discharge bubbles accumulated in a flow passage in order to drive pressure generating means of all nozzles by giving a uniform driving signal thereto while driving a sucking means. <P>SOLUTION: The image forming apparatus performs an operation to discharge liquid droplets from the nozzles 104 by causing a pressure variation (expansion or contraction of the internal capacity of a liquid chamber) in a liquid chamber 106 by providing a maintenance driving waveform to the piezoelectric element 121 of a recording head 34 while performing head suction to suck an ink by operating a suction pump 220 with the nozzle surface 34a of the recording head 34 capped by a sucking cap 82a. In this instance, the rows of the plurality of nozzles 104 in communication with one common liquid chamber 108 of the recording head 34 are divided into three blocks a, b, c, with the maintenance driving waveform provided by each block unit. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to a recovery operation in an image forming apparatus including a recording head that ejects droplets.

  In general, a printer, a fax machine, a copier, a plotter, or an image forming apparatus that combines a plurality of these functions includes, for example, a recording head composed of a liquid ejection head that ejects ink droplets, It is also referred to as “paper”, but the material is not limited, and a recording medium, recording medium, transfer material, recording paper, etc. are also used synonymously.) Some perform formation (recording, printing, printing, and printing are also used synonymously). For example, an ink jet recording apparatus as such an image forming apparatus has come to be used in an industrial system such as a textile printing apparatus.

  The “image forming apparatus” means an apparatus for forming an image by discharging a liquid onto a medium such as paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, ceramics, etc. In addition to providing an image having a meaning such as a figure to a medium, it also includes a device for applying an image having no meaning such as a pattern to the medium (simply ejecting droplets). The “ink” is not limited to so-called ink, and is not particularly limited as long as it becomes liquid when ejected, and includes, for example, a DNA sample, a resist, a pattern material, and the like. Used as a general term for liquids.

  In addition, as an image forming apparatus including a liquid discharge head, a serial type image recording apparatus that performs recording by mounting a recording head on a carriage and moving the recording head in a main scanning direction orthogonal to a sheet feeding direction, and an abbreviation of a recording area. There is a line-type image recording apparatus using a line-type head in which a plurality of discharge ports (nozzles) for discharging droplets over the entire width are arranged.

  When image formation is repeated in such an image forming apparatus, paper dust or the like may adhere to the nozzles of the recording head, resulting in ejection failure or ejection failure due to nozzle clogging. Even if a recovery operation such as nozzle suction by the maintenance recovery mechanism is performed on the recording head to which paper dust or the like is attached, it is difficult to remove the paper dust.

  Therefore, as described in Patent Documents 1 to 3, the actuator of the recording head (pressure generating means) is driven while the suction means is driven so that the suction force and the pushing force are applied to the ink or the like in the vicinity of the nozzle holes. It is known to perform recovery operations.

JP 2007-136989 A JP 2001-260393 A JP 2007-90578 A

  However, when performing a recovery operation in which the suction means is driven and the pressure generating means is driven so that the suction force and the pushing force are applied to the ink or the like in the vicinity of the nozzle holes, the pressure generation means of all the nozzles is conventionally used. On the other hand, since driving is performed by giving a uniform drive signal, there is a problem that a sufficient recovery effect cannot be obtained. In particular, when trying to eliminate bubbles and dust remaining in the nozzle, pressure chamber, and common liquid chamber with this recovery method, bubbles in the position of the standing wave of pressure generated in the pressure chamber and common liquid chamber There is a possibility that discharge cannot be promoted. In such a case, the recovery operation must be performed a plurality of times until the image quality is improved, resulting in a problem that wasteful consumption of ink and recovery time are required.

  The present invention has been made in view of the above problems, and an object of the present invention is to enable air bubbles to be reliably discharged in a short time with a smaller amount of ink consumption.

In order to solve the above problems, an image forming apparatus according to the present invention provides:
A plurality of nozzles for discharging ink droplets, each pressure chamber communicating with each nozzle, and a recording head having pressure generating means for generating pressure in each pressure chamber;
A maintenance and recovery mechanism for capping the nozzle surface of the recording head with a cap member and sucking ink from the nozzle;
While capping with the cap member and sucking ink from the nozzles, the pressure generating means corresponding to the plurality of nozzles is predetermined for each of a plurality of blocks including a plurality of predetermined nozzles. And a means for driving with a drive signal of the drive frequency.

  Here, the driving frequency when driving the pressure generating means of at least one block may be different from the driving frequency when driving the pressure generating means of other blocks.

  Moreover, it can be set as the structure which changes the drive frequency when driving the said pressure generation means about one block.

  The drive frequency may include at least a frequency that is substantially the same as the natural frequency of the pressure chamber.

  The drive frequency may include at least a frequency that is an integer multiple of the natural frequency of the pressure chamber or a frequency that is (1 / integer) times the natural frequency of the pressure chamber.

  The drive frequency may include a frequency that is substantially the same as the natural frequency of a common liquid chamber that supplies ink to at least a plurality of pressure chambers.

  The drive frequency may include at least a frequency that is an integer multiple of the natural frequency of the common liquid chamber or a frequency that is (1 / integer) times the natural frequency of the common liquid chamber.

  According to the image forming apparatus according to the present invention, while the ink is sucked from the nozzle by capping with the cap member, the plurality of blocks including a plurality of predetermined nozzles are divided into a plurality of nozzles in a block unit. Since the corresponding pressure generating means is driven, bubbles can be reliably discharged in a short time with a smaller ink consumption.

1 is a schematic side view illustrating an overall configuration of a mechanism unit of an image forming apparatus according to the present invention. It is principal part plane explanatory drawing of the mechanism part. FIG. 4 is a cross-sectional explanatory view in the longitudinal direction of the liquid chamber showing an example of a liquid discharge head constituting the recording head of the image forming apparatus. FIG. 6 is a cross-sectional explanatory view of the liquid discharge head in the lateral direction of the liquid chamber. 2 is a schematic explanatory diagram of a maintenance / recovery mechanism of the image forming apparatus. FIG. FIG. 2 is a block explanatory diagram illustrating an overview of a control unit of the image forming apparatus. 2 is a block diagram illustrating an example of a print control unit and a head drive unit of the control unit. FIG. It is explanatory drawing with which it uses for description of the cleaning operation | movement in 1st Embodiment of this invention. It is explanatory drawing with which it uses for description of the block division | segmentation of a recording head similarly. It is explanatory drawing with which it uses for description of the cleaning operation | movement in 2nd Embodiment of this invention. It is explanatory drawing which shows an example of the drive waveform for a maintenance. It is explanatory drawing which shows the other example of the drive waveform for a maintenance. It is explanatory drawing with which it uses for description of the cleaning operation | movement in 3rd Embodiment of this invention. It is explanatory drawing with which it uses for description of the cleaning operation | movement in 4th Embodiment of this invention. It is explanatory drawing with which it uses for description of the cleaning operation | movement in 4th Embodiment of this invention.

Embodiments of the present invention will be described below with reference to the accompanying drawings. First, an example of an image forming apparatus according to the present invention will be described with reference to FIGS. FIG. 1 is an explanatory side view for explaining the overall configuration of the image forming apparatus, and FIG. 2 is an explanatory plan view of a main part of the apparatus.
This image forming apparatus is a serial type ink jet recording apparatus, and a carriage 33 is slidable in a main scanning direction by main and sub guide rods 31 and 32 which are guide members horizontally mounted on the left and right side plates 21A and 21B of the apparatus main body 1. It is held and moved and scanned in the direction indicated by the arrow (carriage main scanning direction) in FIG. 2 via a timing belt by a main scanning motor (not shown).

  The carriage 33 is provided with recording heads 34a and 34b composed of liquid ejection heads for ejecting ink droplets of yellow (Y), cyan (C), magenta (M), and black (K). The “recording head 34” is arranged in a sub-scanning direction orthogonal to the main scanning direction, and the ink droplet ejection direction is directed downward.

  Each of the recording heads 34 has two nozzle rows. One nozzle row of the recording head 34a has black (K) droplets, the other nozzle row has cyan (C) droplets, and the recording head 34b has one nozzle row. One nozzle row ejects magenta (M) droplets, and the other nozzle row ejects yellow (Y) droplets. As the recording head 34, a recording head having a nozzle row of each color in which a plurality of nozzles are arranged on one nozzle surface can be used.

  Further, the sub tanks 35a and 35b, which are sub tanks as the second ink supply unit for supplying ink of each color corresponding to the nozzle row of the recording head 34, are referred to as the “sub tank 35” when they are not distinguished. ) Is installed. In the sub tank 35, ink cartridges (main tanks) 10y, 10m, 10c, and 10k of various colors that are detachably attached to the cartridge loading unit 4 are supplied from the ink supply tubes 36 of the respective colors by the supply pump unit 24. The recording liquid is replenished and supplied.

  On the other hand, as a paper feeding unit for feeding the papers 42 stacked on the paper stacking unit (pressure plate) 41 of the paper feeding tray 2, a half-moon roller (feeding) that separates and feeds the papers 42 one by one from the paper stacking unit 41. A separation pad 44 made of a material having a large friction coefficient is provided facing the paper roller 43) and the paper feed roller 43, and the separation pad 44 is urged toward the paper feed roller 43 side.

  In order to feed the paper 42 fed from the paper feeding unit to the lower side of the recording head 34, a guide member 45 for guiding the paper 42, a counter roller 46, a transport guide member 47, and a tip pressure roller. And a holding belt 48 which is a conveying means for electrostatically attracting the fed paper 42 and conveying it at a position facing the recording head 34.

  The transport belt 51 is an endless belt, and is configured to wrap around the transport roller 52 and the tension roller 53 and circulate in the belt transport direction (sub-scanning direction). Further, a charging roller 56 that is a charging unit for charging the surface of the transport belt 51 is provided. The charging roller 56 is disposed so as to come into contact with the surface layer of the transport belt 51 and to rotate following the rotation of the transport belt 51. The transport belt 51 rotates in the belt transport direction of FIG. 2 when the transport roller 52 is rotationally driven through timing by a sub-scanning motor (not shown).

  Further, as a paper discharge unit for discharging the paper 42 recorded by the recording head 34, a separation claw 61 for separating the paper 42 from the conveying belt 51, a paper discharge roller 62, and a spur 63 that is a paper discharge roller. And a paper discharge tray 3 below the paper discharge roller 62.

  A duplex unit 71 is detachably mounted on the back surface of the apparatus body 1. The duplex unit 71 takes in the paper 42 returned by the reverse rotation of the conveyance belt 51, reverses it, and feeds it again between the counter roller 46 and the conveyance belt 51. The upper surface of the duplex unit 71 is a manual feed tray 72.

  Further, a maintenance / recovery mechanism 81 for maintaining and recovering the nozzle state of the recording head 34 is disposed in the non-printing area on one side of the carriage 33 in the scanning direction. The maintenance / recovery mechanism 81 includes cap members (hereinafter referred to as “caps”) 82a and 82b (hereinafter referred to as “caps 82” when not distinguished from each other) for capping the nozzle surfaces of the recording head 34, and nozzle surfaces. A wiper member (wiper blade) 83 for wiping the recording medium, an empty discharge receiver 84 for receiving liquid droplets when performing empty discharge for discharging liquid droplets that do not contribute to recording in order to discharge the thickened recording liquid, and a carriage And a carriage lock 87 for locking 33. A waste liquid tank 100 for storing waste liquid generated by the maintenance recovery operation is mounted on the lower side of the head recovery mechanism 81 in a replaceable manner with respect to the apparatus main body.

  Further, in the non-printing area on the other side of the carriage 33 in the scanning direction, there is an empty space for receiving liquid droplets when performing empty discharge for discharging liquid droplets that do not contribute to recording in order to discharge the recording liquid thickened during recording. A discharge receiver 88 is disposed, and the idle discharge receiver 88 includes an opening 89 along the nozzle row direction of the recording head 34.

  In this image forming apparatus configured as described above, the sheets 42 are separated and fed one by one from the sheet feed tray 2, and the sheet 42 fed substantially vertically upward is guided by the guide 45, and includes the transport belt 51 and the counter. It is sandwiched between the rollers 46 and conveyed, and the leading end is guided by the conveying guide 37 and pressed against the conveying belt 51 by the leading end pressing roller 49, and the conveying direction is changed by approximately 90 °.

  At this time, a positive output and a negative output are alternately repeated with respect to the charging roller 56, that is, an alternating voltage is applied, and a charging voltage pattern in which the conveying belt 51 alternates, that is, in a sub-scanning direction that is a circumferential direction. , Plus and minus are alternately charged in a band shape with a predetermined width. When the paper 42 is fed onto the conveyance belt 51 charged alternately with plus and minus, the paper 42 is attracted to the conveyance belt 51, and the paper 42 is conveyed in the sub-scanning direction by the circular movement of the conveyance belt 51.

  Therefore, by driving the recording head 34 according to the image signal while moving the carriage 33, ink droplets are ejected onto the stopped paper 42 to record one line, and after the paper 42 is conveyed by a predetermined amount, Record the next line. Upon receiving a recording end signal or a signal that the trailing edge of the paper 42 has reached the recording area, the recording operation is finished and the paper 42 is discharged onto the paper discharge tray 3.

  When performing the maintenance and recovery of the nozzles of the recording head 34, the nozzle 33 performs the suction from the nozzles by moving the carriage 33 to a position facing the maintenance and recovery mechanism 81 which is the home position and performing capping by the cap member 82. By performing a maintenance and recovery operation such as an empty discharge operation for discharging droplets that do not contribute to image formation, it is possible to perform image formation by stable droplet discharge.

  Next, an example of the liquid discharge head constituting the recording head 34 will be described with reference to FIGS. 3 is a cross-sectional explanatory diagram along the longitudinal direction of the liquid chamber of the head, and FIG. 4 is a cross-sectional explanatory diagram of the head along the lateral direction of the liquid chamber (nozzle arrangement direction).

  This liquid discharge head includes, for example, a flow path plate 101 formed by anisotropic etching of a single crystal silicon substrate, a vibration plate 102 formed by, for example, nickel electroforming bonded to the lower surface of the flow path plate 101, a flow path The nozzle plate 103 joined to the upper surface of the plate 101 is joined and laminated, and the nozzle communication passage 105 and the pressure chamber (individual liquid chamber), which are the passages through which the nozzles 104 for discharging droplets (ink droplets) communicate with each other. 106, an ink supply port 109 communicating with a common liquid chamber 108 for supplying ink to each pressure chamber 106 through a fluid resistance portion (supply path) 107 is formed.

  In addition, two rows (only one row is shown in FIG. 3) of stacked piezoelectric elements as electromechanical conversion elements that are pressure generating means (actuator means) for pressurizing the ink in the liquid chamber 106 by deforming the diaphragm 102. An element 121 and a base substrate 122 to which the piezoelectric element 121 is bonded and fixed are provided. Note that a column portion 123 is provided between the piezoelectric elements 121. This support portion 123 is a portion formed simultaneously with the piezoelectric element 121 by dividing and processing the piezoelectric element member. However, since the drive voltage is not applied, the support portion 123 becomes a simple support. Further, an FPC cable 126 equipped with a drive circuit (drive IC) (not shown) is connected to the piezoelectric element 121.

  The peripheral edge of the diaphragm 102 is joined to a frame member 130, and the frame member 130 serves as a through-hole 131 and a common liquid chamber 108 that house an actuator unit composed of the piezoelectric element 121 and the base substrate 122. A recess and an ink supply hole 132 for supplying ink from the outside to the common liquid chamber 108 are formed. The frame member 130 is formed by injection molding with a thermosetting resin such as an epoxy resin or polyphenylene sulfite, for example.

  Here, the flow path plate 101 is formed by, for example, subjecting the single crystal silicon substrate having a crystal plane orientation (110) to anisotropic etching using an alkaline etching solution such as an aqueous potassium hydroxide solution (KOH), so that the nozzle communication path 105, The pressure chamber 106 is formed with a recess and a hole, but is not limited to a single crystal silicon substrate, and other stainless steel substrates, photosensitive resins, and the like can also be used.

  The vibration plate 102 is formed from a nickel metal plate, and is manufactured by, for example, an electroforming method (electroforming method). Alternatively, a metal plate or a joining member between a metal and a resin plate may be used. it can. The piezoelectric element 121 and the support post 123 are bonded to the diaphragm 102 with an adhesive, and the frame member 130 is further bonded with an adhesive.

  The nozzle plate 103 forms a nozzle 104 having a diameter of 10 to 30 μm corresponding to each pressure chamber 106 and is bonded to the flow path plate 101 with an adhesive. The nozzle plate 103 is formed by forming a water repellent layer on the outermost surface of a nozzle forming member made of a metal member via a required layer.

  The piezoelectric element 121 is a stacked piezoelectric element (here, PZT) in which piezoelectric materials 151 and internal electrodes 152 are alternately stacked. An individual electrode 153 and a common electrode 154 are connected to each internal electrode 152 drawn out to different end faces of the piezoelectric element 121 alternately. In this embodiment, the ink in the pressure chamber 106 is pressurized using the displacement in the d33 direction as the piezoelectric direction of the piezoelectric element 121. However, the pressure in the d31 direction is used as the piezoelectric direction of the piezoelectric element 121. A configuration may be adopted in which the ink in the pressure chamber 106 is pressurized. Alternatively, a structure in which one row of piezoelectric elements 121 is provided on one substrate 122 may be employed.

  In the liquid discharge head configured as described above, for example, by lowering the voltage applied to the piezoelectric element 121 from the reference potential, the piezoelectric element 121 contracts, and the diaphragm 102 descends to expand the volume of the pressure chamber 106. Then, the ink flows into the pressure chamber 106, and then the voltage applied to the piezoelectric element 121 is increased to extend the piezoelectric element 121 in the stacking direction, and the diaphragm 102 is deformed in the nozzle 104 direction to reduce the volume / volume of the pressure chamber 106. By contracting the volume, the ink in the pressure chamber 106 is pressurized, and ink droplets are ejected (ejected) from the nozzle 104.

  Then, by returning the voltage applied to the piezoelectric element 121 to the reference potential, the diaphragm 102 is restored to the initial position, and the pressure chamber 106 expands to generate a negative pressure. At this time, the pressure chamber 106 changes from the common liquid chamber 108 to the pressure chamber. 106 is filled with ink. Therefore, after the vibration of the meniscus surface of the nozzle 104 is attenuated and stabilized, the operation proceeds to the next droplet discharge.

  Note that the driving method of the head is not limited to the above example (drawing-pushing), and striking or pushing can be performed depending on the direction of the drive waveform.

Next, the maintenance / recovery mechanism 81 in this image forming apparatus will be described with reference to FIG. FIG. 5 is a schematic schematic configuration diagram of the maintenance and recovery mechanism.
In the maintenance / recovery mechanism 81, the caps 82 a and 82 b held by the cap holder 212, the wiper member 83 including an elastic body, and the wiper cleaner 86 are held up and down (movable up and down) by the maintenance device frame 211. Has been.

  A cylindrical empty discharge receiver 84 is disposed between the wiper member 83 and the suction cap 82a. The upper end of the empty discharge receiver 84 on the wiper member 83 side scrapes ink adhering to the wiper member 83. A wiper cleaner portion 85 to be dropped is formed. When cleaning the wiper member 83, the wiper member 83 is lowered while the wiper member 83 is pressed against the wiper cleaner portion 85 by the wiper cleaner 86, so that the ink adhering to the wiper member 83 is scraped off to the empty ejection receiver 84 side. .

  Further, a tubing pump (suction pump) 220 as a suction means is connected to the cap 82a closest to the printing area via a flexible tube 219, and only the cap 82a is suctioned (recovered) and moisturized (hereinafter referred to as the cap 82a). It is simply referred to as “suction cap”), and the cap 82b is simply a moisture retention cap. Therefore, when performing the recovery operation of the recording head 34, the recording head 34 that performs the recovery operation is selectively moved to a position where it can be capped by the suction cap 82a.

  A cam shaft 221 that is rotatably supported by the frame 211 is disposed below the caps 82a and 82b, the wiper member 83, and the like, and a cap cam 222 for raising and lowering the cap holder 212 is disposed on the cam shaft 221. A wiper cam 224 for raising and lowering the wiper member 83, a roller 226 as a rotating body to which liquid droplets idled in the idle discharge receptacle 84 are applied, a cleaner cam 228 for swinging the wiper cleaner 86, and a carriage lock Carriage lock cams 229 for moving up and down 87 are provided.

  In order to rotationally drive the suction pump 220 and the cam shaft 221, the rotation of the motor 231 is meshed with the motor gear 232 provided on the motor shaft 231 a and the pump gear 233 provided on the pump shaft 220 a of the suction pump 220 is further engaged. An intermediate gear 236 with a one-way clutch 237 is meshed with an intermediate gear 234 integral with the intermediate gear 233, and the intermediate gear 238 coaxial with the intermediate gear 236 is fixed to the camshaft 221 via the intermediate gear 239. The cam gear 240 is engaged. The intermediate shaft 241 that is the rotation shaft of the intermediate gears 236 and 238 with the clutch 237 is rotatably held by the frame 211.

  In this maintenance / recovery mechanism 81, when removing ink and impurities adhering to the surface (nozzle surface) where the nozzles of the recording head 34 are formed, the motor 231 is driven and the wiper blade 83 is raised via the wiper cam 224. In this state, by moving the carriage 33 in the main scanning direction, the wiper blade 83 wipes the nozzle surface of the recording head 34 to wipe away impurities and the like.

  Further, if the nozzles of the recording head 34 are left exposed to the outside air, the ink in the inside dries and thickens and adheres, and the ink ejection performance is deteriorated. To prevent this, the recording head 34 is prevented. When the nozzle surface is covered with the cap 82, the motor 231 is rotated, the cap 82 is raised via the cap cam 213, and the nozzle surface of the recording head 34 is capped.

Next, an outline of the control unit of the image forming apparatus will be described with reference to FIG. This figure is an overall block diagram of the control unit.
The control unit 500 temporarily stores a CPU 511 that also serves as a means for controlling the recovery operation according to the present invention, which controls the entire apparatus, a ROM 502 that stores programs executed by the CPU 511 and other fixed data, image data, and the like. RAM 503 for storing, rewritable nonvolatile memory 504 for holding data even while the power of the apparatus is shut off, image processing for performing various signal processing and rearrangement on image data, and other control of the entire apparatus And an ASIC 505 for processing input / output signals.

  Further, a print control unit 508 including a data transfer unit for driving and controlling the recording head 34 and a driving signal generating unit, a head driver (driver IC) 509 for driving the recording head 34 provided on the carriage 33 side, An AC bias is applied to the charging roller 56, a main scanning motor 554 that moves and scans the carriage 33, a sub-scanning motor 555 that rotates and moves the conveyor belt 51, a motor drive unit 510 that drives the maintenance / recovery motor 231 of the maintenance / recovery mechanism 81. An AC bias supply unit 511 and the like are provided.

  The control unit 500 is connected to an operation panel 514 for inputting and displaying information necessary for the apparatus.

  The control unit 500 has an I / F 506 for transmitting and receiving data and signals to and from the host side, an information processing device such as a personal computer, an image reading device such as an image scanner, an imaging device such as a digital camera, and the like. From the host 600 side via the cable or network via the I / F 506.

  The CPU 501 of the control unit 500 reads and analyzes the print data in the reception buffer included in the I / F 506, performs necessary image processing, data rearrangement processing, and the like in the ASIC 505, and prints the image data. The data is transferred from the unit 508 to the head driver 509. Note that generation of dot pattern data for image output is performed by the printer driver 601 on the host 600 side.

  The print control unit 508 transfers the above-described image data as serial data, and outputs a transfer clock, a latch signal, a control signal, and the like necessary for transferring the image data and confirming the transfer to the head driver 509. Including a D / A converter for D / A converting D / A conversion of drive pulse pattern data stored in the ROM, a voltage signal amplifier, a current amplifier, and the like, and a drive signal or a plurality of drive pulses Is output to the head driver 509.

  The head driver 509 selectively selects droplets of the recording head 7 as drive pulses constituting a drive signal given from the print control unit 508 based on image data corresponding to one line of the recording head 34 inputted serially. The recording head 7 is driven by applying it to a driving element (for example, a piezoelectric element) that generates energy to be discharged. At this time, by selecting a driving pulse constituting the driving signal, for example, dots having different sizes such as a large droplet, a medium droplet, and a small droplet can be sorted.

  The I / O unit 513 acquires information from various sensor groups 515 mounted on the apparatus, extracts information necessary for controlling the printer, and print control unit 508, motor control unit 510, AC bias supply unit Used to control 511. The sensor group 515 includes an optical sensor for detecting the position of the paper, a temperature / humidity sensor (environmental sensor) for detecting the temperature and humidity in the apparatus, a sensor for monitoring the voltage of the charging belt, and an interface for detecting opening and closing of the cover. There are lock switches and the like, and the I / O unit 513 can process various sensor information.

Next, an example of the print control unit 508 and the head driver 509 will be described with reference to FIG.
As described above, the print control unit 508 generates and outputs a common drive waveform (drive waveform for image formation) composed of a plurality of drive pulses (drive signals) within one printing cycle at the time of image formation, and maintains and recovers it. A drive waveform generation unit 701 that generates and outputs a common drive waveform (maintenance drive waveform) composed of sinusoidal drive signals within one drive cycle during operation (maintenance operation), and a 2-bit corresponding to a print image A data transfer unit 702 that outputs image data (gradation signals 0 and 1), a clock signal, a latch signal (LAT), and droplet control signals M0 to M3 is provided.

  The droplet control signal is a 2-bit signal that instructs each droplet to open and close the analog switch 715 that is a switch unit of the head driver 209. The droplet control signal is a waveform to be selected according to the printing cycle of the common drive waveform. State transition to ON), and state transition to L level (OFF) when not selected.

  The head driver 509 receives a transfer clock (shift clock) from the data transfer unit 702 and serial image data (gradation data: 2 bits / 1 channel (1 nozzle)), and register values of the shift register 711. Is latched by a latch signal, a decoder 713 that decodes gradation data and control signals M0 to M3 and outputs the result, and a logic level voltage signal of the decoder 713 is a level at which the analog switch 715 can operate. A level shifter 714 for level conversion to an analog switch 716 and an analog switch 716 that is turned on / off (opened / closed) by the output of the decoder 713 provided via the level shifter 714 are provided.

  The analog switch 715 is connected to the selection electrode (individual electrode) 154 of each piezoelectric element 121, and the common drive waveform from the drive waveform generation unit 701 is input thereto. Accordingly, when the analog switch 715 is turned on in accordance with the result of decoding the serially transferred image data (gradation data) and the control signals MN0 to MN3 by the decoder 713, a required drive signal constituting the common drive waveform is obtained. Passing (selected) is applied to the piezoelectric element 121.

  Here, when performing a maintenance operation for maintaining and recovering the performance of the recording head 34, the CPU 501 of the control unit 500 controls the drive of the maintenance / recovery mechanism 81 and performs a maintenance drive waveform for the drive waveform generation unit 701. And the image data for driving each pressure generating means (actuator: piezoelectric element 121 in this example) of the recording head 34 is given to the data transfer unit 702, so that the maintenance driving waveform of the recording head 34 is controlled. Recovery operation control for driving each piezoelectric element 121 to cause a pressure change in the liquid chamber 106 is performed.

Next, the cleaning operation of the recording head maintenance / recovery operation according to the first embodiment of the present invention will be described with reference to FIGS. FIG. 8 is an explanatory diagram for explaining the cleaning operation, and FIG. 9 is an explanatory diagram for explaining the block division.
First, in the cleaning operation in the maintenance and recovery operation, as described above, the ink is discharged from the nozzle 104 of the recording head 34 by operating the suction pump 220 with the nozzle surface 34a of the recording head 34 capped by the suction cap 82a. By sucking and wiping off the ink adhering to the nozzle surface 34a by the wiper blade 83 and sucking and discharging the ink in the suction cap 82a, the ejection performance of the nozzle 104 of the recording head 34 is maintained and recovered.

  Here, as shown in FIG. 9A, while the nozzle surface 34a of the recording head 34 is capped with the suction cap 82a, the suction pump 220 is operated to perform the head suction for sucking ink. As shown in FIG. 4B, a maintenance drive waveform is applied to the piezoelectric element 121 which is a pressure generating means of the recording head 34 to change the pressure in the liquid chamber 106 (expand or shrink the volume in the liquid chamber). ) And the operation of ejecting droplets from the nozzle 104 is also performed.

  At this time, as shown in FIG. 9, a plurality of (three nozzles in this example) blocks a, b, and c are arranged in a plurality of nozzles 104 (nozzle rows) communicating with one common liquid chamber 108 of the recording head 34. As shown in FIG. 8B, a maintenance drive waveform is given for each block. The number of blocks is not limited to three and may be two or four or more.

  Here, as shown in FIG. 8B, as a driving order by applying a driving waveform for maintenance to the piezoelectric elements (pressure generating means) of each block, first, the central block b is driven, and then, Driving is in the order of block a and block c (which may be reversed).

  In other words, the common liquid chamber 108 of the liquid discharge head constituting the recording head 34 is configured to flow ink from the center toward both ends as shown in FIG. In the case of such a common liquid chamber configuration, the ink flow tends to stay in the vicinity of the center where the flows are separated. For this reason, air bubbles and foreign matters are likely to remain here. In order to efficiently discharge this, first, the pressure chamber 106 corresponding to the vicinity of the center of the common liquid chamber 108 is driven to move bubbles and foreign substances upstream of the flow to the vicinity of the end of the common liquid chamber 108. . Next, by driving the pressure chamber 108 corresponding to the end of the common liquid chamber 108 in the order of the blocks a and c (or the reverse order), these bubbles and foreign matters are retained near the center of the common liquid chamber 108. It can be made to flow without.

  As before, when the maintenance drive waveform is simultaneously applied to all the nozzles, there is a high possibility that bubbles in the pressure chamber 106 and the common liquid chamber 108 cannot be expelled. On the other hand, the position of the node of the standing wave of the pressure generated in the pressure chamber 106 and the common liquid chamber 108 is changed by dividing a plurality of nozzles into required blocks and driving them sequentially or randomly for each block. It is possible to change the position where the bubbles stay, thereby facilitating the discharge of the bubbles.

  In addition, the drive waveform for maintenance is not only shrinking the volume in the pressure chamber (decrease in pressure) but also in a waveform that causes contraction and expansion (for example, sine wave etc.), not only discharge of bubbles, For example, it is possible to remove foreign matter adhering to the vicinity of the nozzle.

  Further, as a condition for giving a driving waveform for maintenance to the piezoelectric element 121 of the recording head 34, as shown in FIG. 8B, the elapsed time (waiting time) n1 from the start of the head suction, the number of times of driving (droplets to be ejected) The number n2 (droplet)), the time interval n3 between the blocks can be determined in advance, or can be determined according to the environmental conditions detected by the environmental sensor, the number of printed sheets, or the like.

  In this way, while the ink is sucked from the nozzle by capping with the cap member, the pressure generating means corresponding to the plurality of nozzles is driven in units of blocks for a plurality of blocks configured with a plurality of predetermined nozzles. With this configuration, it is possible to reliably discharge bubbles in a short time with a smaller amount of ink consumption.

Next, the cleaning operation of the recording head maintenance / recovery operation according to the second embodiment of the present invention will be described with reference to FIG. FIG. 10 is an explanatory diagram for explaining the cleaning operation. The block division is the same as in FIG.
Here, the driving is performed a plurality of times for each block. In this case, the central block b is always driven, and the time for simultaneously driving the block a and the block b and the time for simultaneously driving the block c and the block b are set. By doing so, the position where the bubbles stay in the common liquid chamber 108 can be moved, and a more effective recovery operation can be performed.

Here, the maintenance drive waveform applied to the recording head 34 in parallel with the head suction will be described.
As the maintenance drive waveform, a sinusoidal drive waveform is used as shown in FIG. The period of the maintenance drive waveform is substantially the same as the natural vibration period Tc in the pressure chamber 106 of the recording head 34.

  As a result, the pressure change in the pressure chamber 106 of the recording head 34 can be substantially maximized, and the pressure applied to the nozzle 104 can be increased and recovered with a high recovery rate. That is, by setting the frequency of the driving waveform (driving signal) for driving the pressure generating means of the recording head to be substantially the same as the natural vibration frequency of the pressure chamber, it is possible to further promote the discharge of bubbles in the pressure chamber. .

  In addition, as shown in FIG. 12, the drive cycle (drive frequency) of the maintenance drive waveform applied to each of the blocks a, b, and c can be made different. In this way, the recovery effect is further improved. That is, the recovery effect can be further enhanced by adopting a configuration in which the driving frequency when driving the pressure generating means of at least one block is different from the driving frequency when driving the pressure generating means of other blocks.

Next, the cleaning operation of the recording head maintenance / recovery operation according to the third embodiment of the present invention will be described with reference to FIG. FIG. 13 is an explanatory diagram showing the relationship between the timing at which the maintenance drive waveform is applied to each block and the cycle of the drive waveform for explaining the cleaning operation. The block division is the same as in FIG.
Here, the maintenance drive waveform P1 having the same period (substantially the same frequency as the natural vibration frequency) as the natural vibration period Tc in the pressure chamber 106 of the recording head 34 is applied to the block a and the block c. On the other hand, the block b includes a maintenance drive waveform P1 having substantially the same period as the natural vibration period Tc, a maintenance drive waveform P2 having a period twice (integer multiple) the natural vibration period Tc, and 1/2 of the natural vibration period Tc. A maintenance drive waveform P3 having a period of double (= 1 / integer multiple) is sequentially applied. In FIG. 13, the maintenance drive waveforms P1 to P3 are illustrated at the non-drive positions, but this is for convenience of illustration and is applied corresponding to the drive. The same applies to FIG.

  Thus, the recovery effect can be further enhanced by driving at least one block using a maintenance drive waveform having a different period (drive frequency) from the other blocks. In addition, a maintenance drive waveform having a frequency substantially the same as the natural frequency of the pressure chamber, a maintenance drive waveform having a frequency substantially the same as an integer multiple of the natural frequency of the pressure chamber, and a (1 / integer multiple) of the natural frequency of the pressure chamber. By using a maintenance drive waveform having substantially the same frequency as that of the nozzle, it is possible to change the position of the node of the standing wave of the pressure generated particularly in the pressure chamber, and to further improve the bubble discharge performance.

Next, the cleaning operation of the recording head maintenance / recovery operation according to the fourth embodiment of the present invention will be described with reference to FIG. FIG. 14 is an explanatory diagram showing the relationship between the timing at which a maintenance drive waveform is applied to each block for explaining the cleaning operation and the cycle of the drive waveform. The block division is the same as in FIG.
Here, in the driving of a plurality of times in one block, the driving cycle of the maintenance driving waveform for each time is different. In this example, for each of the blocks a, b, and c, the maintenance drive waveform P2 and the period of the natural vibration period Tc have substantially the same period as the period twice the natural vibration period Tc in the pressure chamber 106 of the recording head 34. A maintenance drive waveform P1 having substantially the same period as the maintenance drive waveform P4 having a period substantially the same as one-third of the natural vibration period Tc is sequentially applied.

  In this way, the recovery effect can be further enhanced by driving at least one block using the maintenance drive waveforms having different periods (drive frequencies).

Next, the cleaning operation of the recording head maintenance / recovery operation according to the fifth embodiment of the present invention will be described with reference to FIG. FIG. 15 is an explanatory diagram showing the relationship between the timing at which the maintenance drive waveform is applied to each block and the cycle of the drive waveform for explaining the cleaning operation. The block division is the same as in FIG.
Here, by combining the third embodiment and the fourth embodiment, the drive cycles of the maintenance drive waveforms are different in each drive in a plurality of times in one block, and the order in which the drive cycles appear is different. , Each block is different.

  In this example, for the block a, the maintenance drive waveform P2 having substantially the same period as the period twice the natural vibration period Tc in the pressure chamber 106 of the recording head 34, and the maintenance drive having substantially the same period as the natural vibration period Tc. A maintenance drive waveform P4 having a period substantially the same as the waveform P1 and a period of 1/3 times the natural vibration period Tc is sequentially applied. For the block b, the maintenance drive waveform P1 having the substantially same period as the natural vibration period Tc in the pressure chamber 106 of the recording head 34, and the maintenance drive having the substantially same period as 1/3 times the natural vibration period Tc. The maintenance drive waveform P2 having the same period as the waveform P4 and twice the natural vibration period Tc is sequentially applied. For block c, a maintenance drive waveform P4 having a cycle substantially the same as 1/3 times the natural vibration cycle Tc in the pressure chamber 106 of the recording head 34, and a maintenance cycle having a cycle substantially the same as twice the natural vibration cycle Tc. A maintenance drive waveform P1 having a cycle substantially the same as the drive waveform P2 and the natural vibration cycle Tc is sequentially applied.

  As a result, the bubble discharge performance is further improved and the recovery effect can be further enhanced.

  The combination of the number of blocks, the drive frequency (cycle), and the time interval is not limited to the above embodiment, and the combination may be changed so as to promote the discharge of bubbles in the pressure chamber and common liquid chamber of the recording head. .

  In addition, as a period of the maintenance drive waveform, instead of the natural vibration period Tc of the pressure chamber 106, the maintenance vibration waveform has a natural vibration period of the common liquid chamber 108, an integer multiple thereof, and a period (frequency) that is (1 / integer) multiple. A driving waveform can also be given. Thereby, the position of the node of the standing wave of the pressure generated particularly in the common liquid chamber can be changed, and the bubbles in the common liquid chamber can be discharged more effectively. Further, if the driving waveform for maintenance includes both the natural vibration period Tc of the pressure chamber and the natural vibration period of the common liquid chamber, the effect of discharging bubbles can be further enhanced.

  Further, since the viscosity of the ink changes according to the environmental conditions, it is preferable to change the peak value of the maintenance drive waveform according to the environmental conditions.

  Further, it is preferable that these series of recovery operations are periodically performed according to, for example, printing conditions. It is more preferable to include a control unit that triggers the recovery operation according to the count value of the number of printed sheets.

  In the above embodiment, the printer configuration has been described as the image forming apparatus according to the present invention. However, the present invention is not limited to this, and can be applied to an image forming apparatus such as a printer / fax / copier multifunction machine. Further, the present invention can be applied to an image forming apparatus using a recording liquid or a fixing processing liquid that is a liquid other than ink.

33 ... Carriage 34, 34a, 34b ... Recording head (liquid ejection head)
81 ... Maintenance recovery mechanism 82a ... Cap 104 ... Nozzle 106 ... Pressure chamber (individual liquid chamber)
108 ... Common liquid chamber 121 ... Piezoelectric element (pressure generating means)
508: Print control unit

Claims (7)

A plurality of nozzles for discharging ink droplets, each pressure chamber communicating with each nozzle, and a recording head having pressure generating means for generating pressure in each pressure chamber;
A maintenance and recovery mechanism for capping the nozzle surface of the recording head with a cap member and sucking ink from the nozzle;
While capping with the cap member and sucking ink from the nozzles, the pressure generating means corresponding to the plurality of nozzles is predetermined for each of a plurality of blocks including a plurality of predetermined nozzles. An image forming apparatus comprising: means for driving with a drive signal having a drive frequency of   2. The image forming apparatus according to claim 1, wherein a driving frequency when driving the pressure generating unit of at least one block is different from a driving frequency when driving the pressure generating unit of another block.   The image forming apparatus according to claim 1, wherein a driving frequency for driving the pressure generating unit for one block is changed.   4. The image forming apparatus according to claim 1, wherein the drive frequency includes at least a frequency that is substantially the same as the natural frequency of the pressure chamber.   The drive frequency includes at least a frequency that is an integer multiple of the natural frequency of the pressure chamber or a frequency that is (1 / integer) times the natural frequency of the pressure chamber. 4. The image forming apparatus according to any one of items 3 to 3.   6. The image formation according to claim 1, wherein the drive frequency includes a frequency that is substantially the same as a natural frequency of a common liquid chamber that supplies ink to at least a plurality of pressure chambers. apparatus.   The drive frequency includes at least a frequency that is an integer multiple of the natural frequency of the common liquid chamber or a frequency that is (1 / integer) times the natural frequency of the common liquid chamber. The image forming apparatus according to any one of 1 to 5.

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